The invention relates to a process for machining spectacle lenses by means of a CNC spectacle lens-machining machine.
A process for taking into account, by calculation, the position of a rough-cast lens which has been positioned on a holding head of a rotatable shaft of a CNC installation for grinding spectacle lenses in accordance with a predeterminable contour of the spectacle lens in question, comprising the following steps: measuring the position of the rough-cast lens held on the holding head with respect to the optical axis with regard to the axis of the rotatable shaft and/or the axis position of a cylindrical or prismatic cut or with respect to conventional markings on the rough-cast lens by means of a detection device, converting the measured values into electrical signals by means of a converter before beginning the processing of the spectacle lens, inputting the signals into the control device of the installation and including these signals in the calculation of the predetermined contour of the spectacle lens, if appropriate in the axis position of a cylindrical or prismatic spectacle lens and/or in the decentration values during the CNC grinding of the spectacle lens, is described in DE 195 27 222 C2, in the name of the present applicant.
The installation which is used to carry out this known process has at least one grinding wheel, at least one rotatable shaft with a holding head for a rough-cast lens, at least one control device for the CNC grinding of the rough-cast lens in accordance with a predetermined contour of the spectacle lens, at least one input device, which is connected to the control device, for the predetermined contour of the spectacle lens, the optical values and/or if appropriate the axis position of a cylindrical or prismatic cut and/or the decentration values of the predetermined contour with regard to the optical axis of the rough-cast lens, and a detection device comprising a coaxial optical monitoring system for the optical values and/or if appropriate the axis position of a cylindrical or prismatic cut of the rough-cast lens and/or for conventional markings on the rough-cast lens, a converter for converting the recorded optical values, if appropriate the axis position and/or the conventional markings into electrical signals, the control device for CNC grinding of the rough-cast lens being connected to the converter, the shaft being designed as a hollow shaft and the holding head being of annular design, the detection device being arranged coaxially with respect to the holding shaft in order to detect the position of the rough-cast lens held on the hollow shaft of the holding head with respect to the axis of the hollow shaft, and the control device only being used to grind the rough-cast lens once the values recorded by the detection device have been taken into account.
The installation which operates in accordance with the abovementioned process does not require orientation of the rough-cast lens if it is fitted with its optical axis within permissible deviations on the holding head of the hollow shaft, since these deviations are captured by the optical monitoring system, are passed via the converter to the CNC control unit for the peripheral grinding of the rough-cast lens, where they are converted into corresponding correction values during grinding. In addition, the optical values and/or if appropriate the axis position of a cylindrical or prismatic cut of the rough-cast lens held on the holding head and/or for conventional markings on the rough-cast lens held by the holding head are taken into account in the CNC control unit for grinding the rough-cast lens, without the rough-cast lens having to be oriented in any way with respect to these values. The detection device may comprise a vertex refractionometer or a similar appliance, which can be used to record the optical values and, if appropriate, the axis position of a cylindrical or prismatic cut of the rough-cast lens held by the holding head. The detection device may also comprise an optical or opto-electronic monitoring system, which can be used to detect conventional markings provided by dots, crosses or the like on the rough-cast lens.
During the machining of the optical surfaces and/or of the edge of spectacle lenses, in particular during the high-performance machining which is becoming increasingly important, and in particular for spectacle lenses which are only held on one side on the holder, the forces which occur during machining can cause displacements of the spectacle lens. These displacements may lead to the rough-cast lens becoming offset with respect to the axis of rotation and!or being rotated, i.e. the angular position of the rough-cast lens changing with respect to the holder. If this displacement is not noticed, the finished spectacle lens is unusable, since either its optical values do not correspond to the required or input values or the decentration does not correspond to the input values. It may also arise that the axial position of a cylindrical or prismatic cut, the position of a near portion or the angular position of the progression channel of a continuous vision lens do not correspond to the input values.